1. Field of the Invention
The present invention relates generally to a blast effects suppression system used to control the damage associated with explosive devices, and more particularly to a system which dispenses water or a similar substance in such a way as to limit the blast and incendiary damage to buildings and other structures, vehicles, and individuals from bombs, especially large vehicle bombs.
2. Description of Related Art
Terrorist acts often involve the use of explosive devices or bombs. One particularly damaging type of bomb is referred to as a large vehicle bomb (LVB). This type of bomb involves a large to extremely large explosive charge placed within a vehicle, such as a car or truck. The explosive charge may utilize any of a wide range of explosives, such as plastic explosives like Composition C4, cast explosives like TNT, or a mixture of ammonium nitrate and organic fuel. LVBs are often placed in proximity to important buildings, such as government buildings, buildings with high values in the eyes of the community, buildings containing critical assets, or inside parking structures.
Much of the damage associated with LVBs is related to the fact that a detonation or explosion creates what is known as air shock waves (also referred to as air shock) and air blast, and associated incendiary effects. Air shock are the very high speed initial shock waves in the form of a high amplitude, short duration compressive wave which moves radially outward through the air from the source of the explosion. The incident short-time pressure rise associated with air shock can be on the order of 10-10,000 or more pounds per square inch (psi), depending on the distance to the charge, and consequently can be very devastating to surrounding objects. The shock waves heat the air to hundreds or thousands of degrees. Furthermore, duration of this very damaging overpressure may be milliseconds or more, and significant impulse is associated with such a shock wave.
On the other hand, air blast can be described as the outward flow of air set in motion by the air shock waves, as well as large quantities of hot explosive products (gases and particulates) from the bomb. This form of overpressure can cause pressures in the range of from 10-1000 pounds per square inch to be reached in fractions of a second, with this overpressure being maintained for a notable duration of time. Secondary damage is also caused by bomb-generated debris and fragmentation, as well as the hot, expanding bomb gases and particulates known as the fireball.
The devastation associated with the explosive blast of LVBs is well known. For example, while a 2000 pound explosive weight truck bomb may generate a fireball 30 meters in diameter, a 5000 pound explosive weight truck bomb may generate a fireball 100 meters in diameter, and can damage structures even miles away. Due to the size of the explosive charge associated with LVBs, it can readily be appreciated that buildings and other permanent structures are severely damaged, not to mention the vehicles either parked or driving in the immediate vicinity of the bomb blast. Furthermore, due to the intensity of the blast, it is not uncommon for such explosions to result in the loss and maiming of human life.
Due to the potential severity of bomb damage, there have been numerous attempts at providing blast suppression systems. The approaches can be grouped generally into three categories. The first type of suppression system utilizes a frangible container positioned directly adjacent the bomb, with the container being filled with a bulk quantity of liquid, particularly water. When explosion occurs, the violence of the detonation breaks open the container thereby releasing the predetermined amount of liquid, which mixes with expanding explosion gases to limit overpressure and fireball effects. An example of this approach is disclosed in Barrett, U.S. Pat. No. 4,836,079.
However, the actual amount of suppressant which thoroughly interacts with the bomb is relatively small, thereby causing this method to be limited to smaller explosive devices due to the weight of, and setup time required to set in place, the requisite quantity of the selected suppressant. Additionally, there is significant expense associated with the manufacture and placement of such containers. Furthermore, utilization of this system normally requires at least some human exposure to the bomb, in order to place the containers, although robots can be used. Still further, this blast suppression mechanism operates post-incident, meaning that the blast suppression system only deploys due to an explosion.
The second type of suppression system involves a sensor-activated water or fire suppressant system. This type of system has been designed generally to suppress blast and incendiary effects from explosions resulting from the rapid combustion of liquid or gaseous fuel-type materials in enclosed areas, as opposed to the explosion or detonation of explosives in open or confined areas. Examples of this approach are disclosed in Bragg, U.S. Pat. No. 5,224,550, Cooper, U.S. Pat. No. 5,254,237, Sapko et al, U.S. Pat. No. 5,119,877, and Moore et al, U.S. Pat. No. 4,597,451.
However, the costs associated with such systems are prohibitively expensive when a large-scale protection of geographic areas of importance is attempted. Furthermore, in the event of an explosion, the blast effects happen too rapidly for such systems to feasibly react in time to effectively suppress them. Once again, the type of blast suppression is post-incident, meaning that the blast suppression system is activated and operates only after an explosion has actually occurred.
The third type of suppression system involves the generation and placement of a foam (usually aqueous) into the area containing the suspected explosive device. These foams are typically dispersions of water and a foaming agent, with water and entrapped air serving as the main active ingredients in the suppression system. Suspensions of water bubbles (films) and foam-carried droplets are known to be effective by interacting with the initial shockwave and by cooling the shocked air. Examples of this approach is disclosed in Moxon et al, U.S. Pat. No. 4,964,329, Clark et al, U.S. Pat. No. 4,589,341, and Graham et al, U.S. Pat. No. 4,543,872.
While, these foaming methods have produced good results, especially with relatively small bombs, the volume of foam needed for LVBs is a concern. The time required to create and maintain large volumes of foam can be considerable. Furthermore, the stability of such foam can easily be compromised by environmental conditions, such as temperature, wind or precipitation. Another problem unique to foam systems is that the presence of the foam obscures the actual bomb from view, thereby creating a more difficult situation for the bomb technicians. For example, for greatest effectiveness the foam must be placed on a specific suspect vehicle or package to reduce the damage from its explosion, thereby obscuring the object from view.
It is thus apparent that the need exists for a device or system for suppression of bomb blast effects, especially for large bombs such as LVBs, which overcomes the problems associated with the prior art. Such a device or system should be capable of being used in both the open-air and in enclosed structures, and should be able to be practically deployed in advance of a potential explosion near critical structures.